Thing is: I want one best Leica lens I can afford. That would be current Summicron 50mm, of course secondhand. If I need to go with compromise, then it would be better to go with new Voiglaender lens. So, only one, but Leica. Other lenses probably will be Voigtlaender. There is no point to go to older and cheaper Leica lenses because new Voigtlaenders are almost same priced and same or even better quality than old Leica lenses. Atleast that is what I could hear and read.

The best Leica 50mm right now is the new Summilux which apparently performs slightly better than the Summicron at all apertures ;-).

If you are going to get a 50/f2, get a good example of the slightly older black Summicron version without a built-in hood, but WITH the focusing lever. My understanding is that the optics in this version are the same as the current model with the built-in hood, but in a lighter more compact lens form, and this lens is generally cheaper on the used market than the latest model. The even earlier black 50mm without hood or focusing lever is apparently a slightly older optical design.